I don't know whether there exists such tools/libraries for time measurements. But it should be not as difficult to write down some test program yourself in a few minutes:

1. Start a timer (f.e. use times(2)).
2. Following lines will be your test. F.e. an if-else statements of 10 conditions. Select f.e. the last condition.
3. Repeat step 2. f.e. 1000000 times.
4. Stop the timer.
5. Build the average of your measured time and the number of cycles.

If you use times(2) starting/stoping the timer is nothing else then just measuring current time while step 5. builds the average of the difference of both measurements and the number of cycles.

In comes down to whether your cases are dense (consecutive) or sparse. If the cases are dense, most compilers will generate a jump table which is very efficient. If the cases are sparse, the compiler will generate an if/else ladder which will probably be a wash.